ArcGIS Engine效率探究之（二）要素的添加和删除、属性的读取和更新（例：面积、周长字段的更新）

原文链接：http://blog.csdn.net/freewaywalker/article/details/23703863

1. 要素的添加

ArcGIS Engine中，主要有两个方法用于要素的添加：

• Using IFeatureClass.CreateFeature followed by IFeature.Store
• Using IFeatureClass.CreateFeatureBuffer with an insert cursor                                                                                                                          

 批量插入feature，如果用feature.store()方法，在图层中一个个地插入要素，较之同时使用insert cursor与feature buffer方法，会慢很多。因为后者触发的事件和复杂行为比较少（比如说没有引发因拓扑关系产生的行为）。（ ArcGIS Engine效率探究之（一）属性的读取中的示例中可见一斑）

2. 要素的删除

删除feature，一个个删除就用IFeature.Delete方法即可，此处不再赘述，只写一种批量删除的方法，用于ITable是针对数据库进行操作的，所以速度很快。

The best approach to take when deleting features depends on two factors, how many features are being deleted and whether the data source is a local geodatabase or an ArcSDE geodatabase.

In the simplest case, a single feature that has already been retrieved can be deleted by callingIFeature.Delete. If bulk features are being deleted and the geodatabase is an ArcSDE geodatabase, the most efficient approach requires the use of a search cursor and the IFeature.Delete method.

On the other hand, if the geodatabase is a local geodatabase (a file or personal geodatabase), the most efficient method for bulk deletion is theITable.DeleteSearchedRows method.

示例：

  ///<summary>
  ///删除某featurelayer中所有feature
  ///</summary>
  ///<param name="pLayer">操作的涂层</param>
  ///<remarks>该方法可以给一个queryfilter，进行删除符合条件的features</remarks>
  private void DeleteAllFeatures(IFeatureLayer pLayer, <code></code>IQueryFilter queryFilter)
  {
    ITable pTable = pLayer.FeatureClass as ITable;
    pTable.DeleteSearchedRows(queryFilter);
  }

3. 属性的读取

方法一：

ITable pTable = pLayer.FeatureClass as ITable;
clsFldValue = pTable.GetRow(i).get_Value(clsFldIndex);

方法二：

IFeatureCursor FCursor = pLayer.FeatureClass.Search(new QueryFilterClass(), false);
IFeature feature = FCursor.NextFeature();
if (feature == null) return null;
clsFldValue = feature.get_Value(clsFldIndex);
feature = FCursor.NextFeature();

4.属性的更新

一、当将一批数据更新为某一相同的属性时，使用ITable.UpdateSearchedRows效率会很高。

示例如下:

// Find the position of the field that will be updated.
int typeFieldIndex = featureClass.FindField("TYPE");

// Create a query filter defining which fields will be updated
// (the subfields) and how to constrain which rows are updated
// (the where clause).
IQueryFilter queryFilter = new QueryFilterClass
{
    SubFields = "TYPE", WhereClause = "LANE_COUNT = 4"
};

    // Create a feature buffer containing the values to be updated.
    IFeatureBuffer featureBuffer = featureClass.CreateFeatureBuffer();
    featureBuffer.set_Value(typeFieldIndex, "Highway");
   

    // Cast the class to ITable and perform the updates.
    ITable table = (ITable)featureClass;
    IRowBuffer rowBuffer = (IRowBuffer)featureBuffer;
    table.UpdateSearchedRows(queryFilter, rowBuffer);
}

二、逐条更新记录

 这种方式中可有三种方法，如下

方法一：

for (int i = 0; i < pTable.RowCount(null); i++)
{
    pRow = pTable.GetRow(i);
    pRow.set_Value(2, i + 6);
    pRow.Store();
}

方法二：

IFeatureCursor FCursor = pLayer.FeatureClass.Search(new QueryFilterClass(), false);
IFeature feature = FCursor.NextFeature();

for (int i = 0; i < featureNum; i++)
{

    feature.set_Value(2, i);
    feature.Store();
    feature = FCursor.NextFeature();
}

方法三：

ICursor pCursor =pTable.Update(null, false);
pRow = pCursor.NextRow();
for (int i = 0; i < pTable.RowCount(null); i++)
{
    pRow.set_Value(2, i + 6);
    pCursor.UpdateRow(pRow);
    pRow = pCursor.NextRow();
}

试验数据为320条记录，三种方法的运行时间为：法（1）为40297ms;法（2）34922ms为;法（3）为219ms.
可见运用IFeature和IRow的Store方法更新速度都很慢，用ICursor 的UpdateRow方法速度很快，分别是前两者效率的184倍、159倍！
实例：

     现有接近20000条多边形要素需要更新面积及周长：

 方法一：

   

int index = FieldIndex(pFeatureClass, name);
                IFeatureCursor pFCursor = pFeatureClass.Update(null,false);
                IFeature pFeature = pFCursor.NextFeature();
                IArea pArea;
                ICurve pCurve;

                while (pFeature != null)
                {
                    
                     if (name=="Shape_Area")
                    {
                        pArea = pFeature.Shape as IArea;
                        pFeature.set_Value(index, pArea.Area);
                    }
                     else
                    {
                        pCurve = pFeature.Shape as ICurve;
                        pFeature.set_Value(index, pCurve.Length);
                    }
                     pFeature.Store();
                    pFeature = pFCursor.NextFeature();
                }
                System.Runtime.InteropServices.Marshal.ReleaseComObject(pFCursor);

 方法二：

int index = FieldIndex(pFeatureClass, name);
                IFeatureCursor pFCursor = pFeatureClass.Update(null,false);
                IFeature pFeature = pFCursor.NextFeature();
                IArea pArea;
                ICurve pCurve;

                while (pFeature != null)
                {
                    
                     if (name=="Shape_Area")
                    {
                        pArea = pFeature.Shape as IArea;
                        pFeature.set_Value(index, pArea.Area);
                    }
                     else
                    {
                        pCurve = pFeature.Shape as ICurve;
                        pFeature.set_Value(index, pCurve.Length);
                    }

                    pFCursor.UpdateFeature(pFeature);
                    pFeature = pFCursor.NextFeature();
                }
                System.Runtime.InteropServices.Marshal.ReleaseComObject(pFCursor);

其实，就是一条语句的差异，但是数据量大时，方法 二的效率要远远高于方法一。